A. Field of the Invention
The present invention relates to a clutch cover assembly, and in particular to a clutch cover assembly provided with a friction surface wear compensation mechanism that maintains a diaphragm spring at a predetermined, generally constant attitude with respect to the clutch cover with the clutch cover assembly in a clutch engaged state.
B. Description of the Background Art
In general, a clutch cover assembly is fixed to a flywheel of an engine, and is used for selectively transmitting torque power from the engine to a transmission through friction facings of the clutch disk assembly that is selectively engaged and dis-engaged from rotation with the flywheel. It is always desirable to increase the life-expectancy of the clutch cover assembly and the clutch disk assembly. For this reason, some clutch disk assemblies have employed friction facings which are fixed to cushioning plates without using rivets for increasing effective thicknesses of the friction facings.
As the friction facings wear, the clutch engagement position of the pressure plate moves closer to the flywheel since the friction facing thickness diminishes. As a result, an attitude or deflection orientation of the diaphragm spring changes as it biases the pressure plate in the clutch engagement position toward the flywheel. As the attitude or orientation of the diaphragm spring changes, the biasing force it imparts against the pressure plate may likewise change. A friction following or compensating mechanism has been employed for preventing change in position of the diaphragm spring due to wear of the friction facings by moving a support member, which supports a side of the diaphragm spring near the clutch cover toward the flywheel, in accordance with the wear. The friction following mechanism includes a wedge mechanism supporting the side of the diaphragm spring near the clutch cover. The wedge mechanism continuously biases the support member toward the diaphragm spring by a centrifugal force or an elastic force of a spring, for instance as shown in U.S. Pat. Nos. 5,586,633, 5,431,268, 5,570,768 and 5,419,418, which are incorporated herein by reference. As the friction facing wears in the clutch cover assembly, the pressure plate moves toward the flywheel. Thereby, the diaphragm spring changes its position. When a releasing or disengaging operation is performed, the diaphragm spring in the changed attitude exerts an altered force. This altered force from the diaphragm spring tends to form a space between a member of the wedge mechanism and the diaphragm spring, and this space is filled by movement of wedge members of the wedge mechanism. In this manner, the initial attitude of the diaphragm spring is kept.
In the conventional structure described above, an amount or distance of movement of the support member supporting the diaphragm spring depends on the load balance between the diaphragm spring and the wedge mechanism, and therefore may not always precisely correspond to the amount or thickness of wear of the friction member. This leads to imprecise compensation of the changes in the diaphragm spring attitude due to wear of the friction member.
In a clutch cover assembly disclosed in U.S. Pat. Nos. 5,586,633 and 5,431,268, the wedge mechanism also includes a fulcrum ring disposed between the clutch cover and the diaphragm spring, a biasing mechanism for biasing the fulcrum ring away from the pressure plate, and a restricting mechanism for preventing movement of the fulcrum ring away from the pressure plate and allowing the fulcrum ring to move a distance, which is equal to an amount of wear caused at the friction facing, axially away from pressure plate. Parts forming the restricting mechanism are engaged with the pressure plate. These parts are specifically a bolt having a head opposed to a side of an arm of the fulcrum ring near the clutch cover, a wedge fixed to the bolt, and a wedge collar disposed radially outside the wedge and inserted into an aperture in the clutch plate. An end of the wedge collar is in contact with a frictional surface of the flywheel. The wedge has an outer peripheral surface which is tapered and diverges toward the flywheel, and the wedge collar has a tapered inner peripheral surface which is in close contact with the tapered surface of the wedge.
In this structure, when a friction facing of the clutch disk assembly wears to some extent, the pressure plate and the fulcrum ring move toward the flywheel with respect to the restricting mechanism supported by the flywheel, so that a space is formed between the head of the bolt and the arm of the fulcrum ring. In a subsequent releasing operation, the fulcrum ring biased by the biasing mechanism moves axially until it is brought into contact with the head of the bolt. As described above, the fulcrum ring axially moves a distance generally equal to an amount of wear with respect to the pressure plate, but the diaphragm spring may not change its attitude with regard to wear of the friction facing.
In the releasing operation before wearing of the friction facing, when the biasing mechanism exerts a load on the bolt, the wedge is axially pulled to spread the wedge collars by the tapered surface, so that a friction between the wedge collar and an inner periphery of the aperture of the wedge plate increases. As a result, movement of the whole restricting mechanism is restricted.
As described above, when wear occurs, the pressure plate moves with respect to the restricting mechanism of which wedge collar is supported by the flywheel. Since the wedge collar is in contact with the friction surface of the flywheel, it is liable to be adversely affected by heat of the flywheel.